1. Field of the Invention
The present invention relates to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive, and, in particular, to an optical disk recording method, an optical disk reproducing method, an optical recording medium using the method, and an optical disk drive for recording data at high density and reproducing the data thus recorded at high density.
2. Description of the Related Art
Recently, as optical recording media (optical disk, magneto-optical disk and so forth) come to have large capacities, low costs, high reliabilities, and so forth, they have become used in various fields such as recording/reproducing of image information, recording/reproducing of various code data in computer systems, and so forth.
Especially, optical disk drives are demanded to have further large capacities, and need to use recording/reproducing methods of recording data at high density, and reproducing with high accuracy the data recorded at high density.
As a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto optical recording media, a method of shortening of laser wavelength and relative shortening of spot diameter through improvement of numerical aperture (NA) have been performed, for example.
Further, as a recording/reproducing method for high-density data recording and high-accuracy data reproducing onto an optical recording medium of a magneto-optical recording system, shortening of record mark through magnetic-field modulation recording has been performed, for example.
In the related art, for optical recording media in the magneto-optical recording system, record marks through magnetic-field modulation recording are recorded successively with portions thereof overlapped with one another, a recording density in a track direction (referred to as a line density, hereinafter) is increased in comparison to a track width, and, thus, the total recording density is increased. Further, the track width is shortened, a recording density in a radial direction (referred to as a track density, hereinafter) is increased, and, thus, the total recording density is also increased.
Thus, in order to increase a recording density, a line density is increased, and/or a track density is increased.
However, when a track density is increased, in a case where interference of diffracted light is used as in a tracking error detecting system employing a push-pull method, a tracking signal is degraded when the track width is shortened to be less than a predetermined width. For example, in a case where a laser wavelength is 650 nm and a numerical aperture is 0.6, the tracking signal is degraded when the track width is less than approximately 0.505 μm. Accordingly, there is a limit of improvement in track density.
When a line density is increased, because record marks are record successively with portions thereof overlapped with one another, crescent patterns of the record marks come to be emphasized. Such crescent record marks have curvature at end portions thereof increased when the track width increases, and portions which are not effective for reproducing increase.
Especially, in a case of MSR (Magnetically-induced Super Resolution) medium of double mask type, the crescent pattern of a record mark and a reproducing aperture (magnetic window) are exactly reverse in curvature. Accordingly, a resulting reproduced signal is degraded.
Thus, there is a limit of increase in recording density for each of the methods of increasing line density and increasing track density.